Christopher P. Hill

Evidence for a Quantum Phase Transition in Pr~2~-~xCe~xCuO~4~-~d~e~l~t~a from Transport Measurements

The doping and temperature dependence of the Hall coefficient, RH, and ab-plane resistivity in the normal state down to 350mK is reported for oriented films of the electron-doped high-Tc superconductor Pr2-xCexCuO4+d. The doping dependence of b (r=r0+AT^b) and R_sub_H (at 350 mK) suggest a quantum phase transition at a critical doping near x=0.165.

Infrared properties of electron-doped cuprates: Tracking normal-state gaps and quantum critical behavior in Pr2 − xCexCuO4

We report the temperature dependence of the infrared-visible conductivity of Pr2 − xCexCuO4 thin films. When varying the doping from a non-superconducting film (x = 0.11) to a superconducting overdoped film (x = 0.17), we observe, up to optimal doping (x = 0.15), a partial gap opening. The magnitude of this gap extrapolates to zero for x ~ 0.17. A model combining a spin density wave gap and a frequency- and temperature-dependent self-energy reproduces our data reasonably well, suggesting the coexistence of magnetism and superconductivity in this material and the existence of a quantum critical point at this Ce concentration.

Charge order to two-dimensional metal crossover in Pr0.5(Sr1−yCay)0.5MnO3

Abstract We report a low-temperature specific heat study of Pr 0.5 (Sr 1− y Ca y ) 0.5 MnO 3 (0 y y =1) to AFM 2D metal ( y =0). A two-phase coexistence for the intermediate compositions is found. The effect of magnetic field on the specific heat of Pr 0.5 Sr 0.5 MnO 3 is also presented and discussed.

Nernst effect in electron-doped Pr 2 − x Ce x CuO 4

The Nernst effect of Pr 2 - x Ce x CuO 4 (x=0,13, 0.15, and 0.17) has been measured on thin film samples between 5-120 K and 0-14 T. In comparison to recent measurements on hole-doped cuprates that showed an anomalously large Nernst effect above the resistive T c and H c 2 [Z. A. Xu et al., Nature (London) 406, 486 (2000); Yayu Wang et al., Phys. Rev. B 64, 224519 (2001); Yayu Wang et al., Phys. Rev. Lett. 88, 257003 (2002); C. Capan et al., ibid. 88, 056601 (2002)], we find a normal Nernst effect above T c and H c 2 for all dopings. The lack of an anomalous Nernst effect in the electron-doped compounds supports the models that explain this effect in terms of amplitude and phase fluctuations in the hole-doped cuprates. In addition, the H c 2 (T) determined from the Nernst effect shows a conventional behavior for all dopings. The energy gap determined from H c 2 (0) decreases as the system goes from underdoping to overdoping in agreement with the recent tunneling experiments.

Optical Properties of (Pr,Ce)2CuO4

We studied the optical conductivity of electron doped Pr1−xCexCuO4 from the underdoped to the overdoped regime. The observation of low to high frequency spectral weight transfer reveals the presence of a gap, except in the overdoped regime. A Drude peak at all temperatures shows the partial nature of this gap. The close proximity of the doping at which the gap vanishes to the antiferromagnetic phase boundary leads us to assign this partial gap to a spin density wave.

Evidence for a Quantum Phase Transition inPr2−xCexCuO4−δfrom Transport Measurements

The doping and temperature dependence of the Hall coefficient, RH, and ab-plane resistivity in the normal state down to 350mK is reported for oriented films of the electron-doped high-Tc superconductor Pr2-xCexCuO4+d. The doping dependence of b (r=r0+AT^b) and R_sub_H (at 350 mK) suggest a quantum phase transition at a critical doping near x=0.165.

Evidence for a quantum phase transition in the electron-doped cuprate Pr2-xCexCuO4+d from Hall and resistivity measurements

The doping and temperature dependence of the Hall coefficient, RH, and ab-plane resistivity in the normal state down to 350mK is reported for oriented films of the electron-doped high-Tc superconductor Pr2-xCexCuO4+d. The doping dependence of b (r=r0+AT^b) and R_sub_H (at 350 mK) suggest a quantum phase transition at a critical doping near x=0.165.